diff --git a/Database/MongoDB/Util.hs b/Database/MongoDB/Util.hs
index ddf9c1c..4de9f5c 100644
--- a/Database/MongoDB/Util.hs
+++ b/Database/MongoDB/Util.hs
@@ -79,5 +79,5 @@ putNull = putI8 0
 putS :: L8.ByteString -> Put
 putS s = putLazyByteString s >> putNull
 
-putStrSz :: L.ByteString -> Put
+putStrSz :: L8.ByteString -> Put
 putStrSz s = putI32 (fromIntegral $ 1 + L.length s) >> putS s